1. Field of the Invention
This invention relates to compositions of matter for and methods of defoliating plants. More specifically, through not be way of limitation, this invention relates to the defoliation of plants such as, for example, cotton.
2. Description of the Prior Art
It has been known for some time that an aqueous solution of an alkali metal chlorate is an effective defoliant. Sodium chlorate is low in cost and readily available, therefore, it generally is preferred. Further, it is known that the defoliant may contain additional additives such as surfactants, fire retardants, corrosion inhibitors and the like, but little if any research in this regard has been conducted in the past.
Defoliation of plants at certain stages in their growth has many advantages. For example, in the case of cotton plants, defoliation enhances the drying of the cotton bolls and improves or at least maintains the quality of the cotton through a reduction of boll rot and a decrease in the straining of the cotton as it is mechanically harvested.
Numerous other types of plant life frequently are defoliated to facilitate harvest such as, for example, rice, sunflower, soybean plants and the like.
Sodium chlorate, however, is a strong oxidizer and greatly accelerates the burning rate of flammable matter. It is for this reason that sodium chlorate should not be used alone as a defoliant because the fire hazard it creates is too great to be tolerated. It has been known, heretofore, to use sodium carbonate as a fire retardant additive to solutions of sodium chlorate. An example of such a combination is disclosed in U.S. Pat. No. 1,534,289.
U.S. Pat. No. 2,704,243 discloses various boron containing compounds for use as fire retardant additives to chlorate solutions. Examples of such boron containing compounds include sodium metaborate, sodium pentaborate and certain other polyborates. However, such boron containing compounds are expensive, thus, their inclusion within the defoliant necessarily increases the cost of the defoliant. Further, boron compounds, even in low concentration, frequently are toxic to plant life and therefore are undesirable in areas that have soils containing naturally occurring high boron concentrations.
In U.S. Pat. No. 1,914,969 it is suggested that certain alkaline earth metal chlorides such as, for example, calcium chloride, are effective fire retardant additives for sodium chlorate solutions. Obviously, of course, continued use of such additives will necessarily result in contamination of the soil with chlorides from the materials which are also undesirable in some areas.
In U.S. Pat. No. 2,749,227 it is suggested that the addition of sodium metaborate to sodium chlorate enhances the defoliant action of the sodium chlorate.
More recently in U.S. Pat. No. 3,867,125, assigned to the same assignee as the present inventor, it is suggested that a combination of an alkali metal carbonate and urea impart greater fire retardancy to a sodium chlorate solution than do either alone and that additional additives such as surfactants may be present. However, this patent fails to provide any indication as to preferable surfactants for addition to sodium chlorate-containing defoliants nor any indication as to the subsequent effectiveness of such a defoliant to which a surfactant has been added.